//
// execution/context_as.hpp
// ~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2022 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef ASIO_EXECUTION_CONTEXT_AS_HPP
#define ASIO_EXECUTION_CONTEXT_AS_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include "asio/detail/config.hpp"
#include "asio/detail/type_traits.hpp"
#include "asio/execution/context.hpp"
#include "asio/execution/executor.hpp"
#include "asio/execution/scheduler.hpp"
#include "asio/execution/sender.hpp"
#include "asio/is_applicable_property.hpp"
#include "asio/query.hpp"
#include "asio/traits/query_static_constexpr_member.hpp"
#include "asio/traits/static_query.hpp"

#include "asio/detail/push_options.hpp"

namespace asio {

#if defined(GENERATING_DOCUMENTATION)

    namespace execution {

    /// A property that is used to obtain the execution context that is associated
    /// with an executor.
    template <typename U>
    struct context_as_t
    {
      /// The context_as_t property applies to executors, senders, and schedulers.
      template <typename T>
      static constexpr bool is_applicable_property_v =
        is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>;

      /// The context_t property cannot be required.
      static constexpr bool is_requirable = false;

      /// The context_t property cannot be preferred.
      static constexpr bool is_preferable = false;

      /// The type returned by queries against an @c any_executor.
      typedef T polymorphic_query_result_type;
    };

    /// A special value used for accessing the context_as_t property.
    template <typename U>
    constexpr context_as_t context_as;

    } // namespace execution

#else // defined(GENERATING_DOCUMENTATION)

    namespace execution {

        template<typename T>
        struct context_as_t {
#if defined(ASIO_HAS_VARIABLE_TEMPLATES)
            template <typename U>
            ASIO_STATIC_CONSTEXPR(bool,
              is_applicable_property_v = (
                is_executor<U>::value
                  || conditional<
                      is_executor<U>::value,
                      false_type,
                      is_sender<U>
                    >::type::value
                  || conditional<
                      is_executor<U>::value,
                      false_type,
                      is_scheduler<U>
                    >::type::value));
#endif // defined(ASIO_HAS_VARIABLE_TEMPLATES)

            ASIO_STATIC_CONSTEXPR(bool, is_requirable = false);

            ASIO_STATIC_CONSTEXPR(bool, is_preferable = false);

            typedef T polymorphic_query_result_type;

            ASIO_CONSTEXPR context_as_t() {
            }

            ASIO_CONSTEXPR context_as_t(context_t) {
            }

#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
 && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
            template <typename E>
            static ASIO_CONSTEXPR
            typename context_t::query_static_constexpr_member<E>::result_type
            static_query()
              ASIO_NOEXCEPT_IF((
                context_t::query_static_constexpr_member<E>::is_noexcept))
            {
              return context_t::query_static_constexpr_member<E>::value();
            }

            template <typename E, typename U = decltype(context_as_t::static_query<E>())>
            static ASIO_CONSTEXPR const U static_query_v
              = context_as_t::static_query<E>();
#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
            //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)

            template<typename Executor, typename U>
            friend ASIO_CONSTEXPR U

            query(
                    const Executor &ex, const context_as_t<U> &,
                    typename enable_if<
                            is_same<T, U>::value
                    >::type * = 0,
                    typename enable_if<
                            can_query<const Executor &, const context_t &>::value
                    >::type * = 0)

#if !defined(__clang__) // Clang crashes if noexcept is used here.
#if defined(ASIO_MSVC) // Visual C++ wants the type to be qualified.
            ASIO_NOEXCEPT_IF((
              is_nothrow_query<const Executor&, const context_t&>::value))
#else // defined(ASIO_MSVC)
            ASIO_NOEXCEPT_IF((
                    is_nothrow_query<const Executor &, const context_t &>::value))
#endif // defined(ASIO_MSVC)
#endif // !defined(__clang__)
                    {
                            return asio::query(ex, context);
                    }
        };

#if defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
 && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
        template <typename T> template <typename E, typename U>
        const U context_as_t<T>::static_query_v;
#endif // defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
        //   && defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)

#if (defined(ASIO_HAS_VARIABLE_TEMPLATES) \
 && defined(ASIO_HAS_CONSTEXPR)) \
 || defined(GENERATING_DOCUMENTATION)
        template <typename T>
        constexpr context_as_t<T> context_as{};
#endif // (defined(ASIO_HAS_VARIABLE_TEMPLATES)
        //     && defined(ASIO_HAS_CONSTEXPR))
        //   || defined(GENERATING_DOCUMENTATION)

    } // namespace execution

#if !defined(ASIO_HAS_VARIABLE_TEMPLATES)

    template<typename T, typename U>
    struct is_applicable_property<T, execution::context_as_t<U> >
            : integral_constant<bool,
                    execution::is_executor<T>::value
                    || conditional<
                            execution::is_executor<T>::value,
                            false_type,
                            execution::is_sender<T>
                    >::type::value
                    || conditional<
                            execution::is_executor<T>::value,
                            false_type,
                            execution::is_scheduler<T>
                    >::type::value> {
    };

#endif // !defined(ASIO_HAS_VARIABLE_TEMPLATES)

    namespace traits {

#if !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
 || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)

        template<typename T, typename U>
        struct static_query<T, execution::context_as_t<U>,
                typename enable_if<
                        static_query<T, execution::context_t>::is_valid
                >::type> : static_query<T, execution::context_t> {
        };

#endif // !defined(ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
        //   || !defined(ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)

#if !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)

        template<typename T, typename U>
        struct query_free<T, execution::context_as_t<U>,
                typename enable_if<
                        can_query<const T &, const execution::context_t &>::value
                >::type> {
            ASIO_STATIC_CONSTEXPR(bool, is_valid = true);

            ASIO_STATIC_CONSTEXPR(bool, is_noexcept =
            (is_nothrow_query<const T &, const execution::context_t &>::value));

            typedef U result_type;
        };

#endif // !defined(ASIO_HAS_DEDUCED_QUERY_FREE_TRAIT)

    } // namespace traits

#endif // defined(GENERATING_DOCUMENTATION)

} // namespace asio

#include "asio/detail/pop_options.hpp"

#endif // ASIO_EXECUTION_CONTEXT_AS_HPP
